Whoa there! The artist may perhaps just be noting that they're family. Hubworld, iTunes, and Netflix summaries, plus the back cover of the Royal Pony Wedding DVD, all mention that Cadance is Princess Celestia's niece...

The merchandise needs to be taken with a grain of salt, of course (until the show team is forced to include it), but the video description/summary that is part of every episode release is something else entirely.

Where on earth did you read that Hasbro claimed all that about the Apple family? I don't want to clog the artist's inbox with an argument, but I think you're way off base here...

I don't have The Hub channel, so I read those video descriptions whenever I download my MLPFIM episodes from iTunes or pull them up on Netflix.

Not to knock your intelligence, but including things mentioned in merchandise is MOST of what you've seen the show team do! The fact that you didn't notice is credit to their care in making a great show despite that. Here's just a few examples of toys if you care to Google them: You see the "Friendship Express Train" and "Twilight Sparkle's Twinkling Balloon" in the show's opening EVERY episode, and "Glimmer Wings Rarity" featured rather prominently in "Sonic Rainboom." Even Applejack getting covered with edible glitter in "Apple Family Reunion" is a version of her special edition metallic sparkle blind bag toy: [link]Plus the majority of the current MLP toy line (particularly at Target) is labeled "Crystal Empire." Sound familiar?

But all that is really to say once again that the MLPFIM team have taken what could have been a giant horrible toy commercial and brought delightful stories to life that have captured hearts around the globe, even as they did the artist who took the time to create the picture that sparked all this. I'll definitely drink to that.